Four component objective lens



SEARCH BQQN Filed May 22, 1967 6 w w m F 0 m 7 m m 2 u G L n O //M/ M m w w w w 7 MICRONS MAX INYENTOR.

REISS ATTORNEYS United States Patent 3,466,116 FOUR COMPONENT OBJECTIVE LENS Max Reiss, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed May 22, 1967, Ser. No. 639,979 Int. Cl. G02b 9/34 US. Cl. 350220 1 Claim ABSTRACT OF THE DISCLOSURE Objective lenses comprising four components, the two outer components being simple negative meniscus elements concave toward the centrally located diaphragm, the front inner component being a positive cemented doublet and the rear inner component being a positive cemented triplet.

This invention relates to seven element, four compo nent lenses, which are well corrected for all aberrations and have high resolution qualities, such as is required for use in microfilm printing. More particularly, this invention relates to lenses comprising four airspaced components, the outer two components being simple negative meniscus elements highly concave toward the centrally located diaphragm, and the two inner components comprising a positive cemented doublet on the front side of the diaphragm and a positive cementedtriplet on the rear side of the diaphragm.

Objective lenses used for micro-imaging must be exceptionally well corrected for all aberrations, and must be capable of extremely high resolution. These high quality requirements for micro-imaging lenses are due to the fact that slight defects, which may be tolerable or even unnoticeable in ordinary objectives, can seriously aifect micro-image quality and may even cause the image to fuse. These quality requirements are particularly difiicult to attain at wide field angles.

It is an object of this invention to provide four component objective lenses which are exceptionally well corrected for spherical aberration, chromatic aberration, coma, astigmatism, field-curvature and distortion.

It is another object of this invention to provide improved four component objectivelenses having sufiiciently high resolution qualities for use in micro-imaging.

Another object of this invention is to provide improved micro-imaging objective lenses adapted to minify the image by a factor ranging approximately from 30:1 to 10:1 with a field coverage of approximately 52".

Further objects and advantages will be found in the details of construction disclosed in the accompanying example and drawings. I

These objects are accomplished according to the present invention by seven element, four component lenses in which the outer two components are simple negative meniscus elements. The use of these simple diverging outer elements permits the lens to cover a field angle of more than 52, while the innertwo converging components compensate for all the various aberrations.

-In the drawings:

FIG. 1 is a sectional view of an objective lens embodying the invention with the long conjugate on the left.

FIG. 2 comprises a set of curves showing the energy distribution of light rays at field angles of (a) 0, (b) 34,

"ice

(c) 46, and (d) 52, all at an aperture of ,f/6 and a magnification factor of 30.

FIG. 3 comprises a set of correction curves for the lens disclosed in Example 1 below showing (a) the spherical aberration curve for the D line of the spectrum, (b) the curves for sagittal and tangential astigmatism, and (c) the curve for distortion.

The lens in FIG. 1 comprises four components, namely an outer pair of dispersive components I and IV encompassing an inner pair of converging components II and III. Components I and IV are both simple negative meniscus elements concave toward the centrally located diaphragm. Component II is a cemented doublet, comprising a front meniscus element and a rear biconvex element. Component III is a cemented triplet comprising from front to rear to biconcave negative element, a biconvex positive element and a meniscus element.

Numerical data for constructing a typical objective lens according to this invention as outlined above is given in the following example, in which the lens elements are numbered from front to rear, N is the index of refraction of each lens element for the D line, V is the index of dispersion, and R, T and S refer respectively to the radii of curvature of the lens surfaces, the thicknesses of the lens elements and the airspaces between the elements numbered by subscript from front to rear:

The curves shown in FIG. 2 are a particularly pertinent criterion of lens performance because they represent the result of tracing hundreds of rays through the lens from point sources at different field angles. The rays traced represent the three primary colors. The quality of the lens is measured by plotting the percentage of light rays from each point source, which are imaged in a spot on the image plane versus the size of the spot. The curves for different field angles give an accurate description of lens quality, since ray tracing is the most accurate method of analyzing a lens without actually constructing a test sample. In addition, the resolution quality of the lens is readily apparent.

As shown by the curves in FIG. 2, the above lens gives exceptional high resolution. For example it will be seen that approximately 75 percent of all the light rays within the maximum field angle of 52 are imaged by the lens within a spot having a diameter of 10 microns. More specifically, when the lens disclosed in Example 1 is used to minify the image by a factor of 30:1, the average resolution is approximately 120 lines per millimeter over most of the image area.

As shown by the curves in FIG. 3, the above lens is corrected to such a degree that spherical aberration for the D line of the spectrum is less than half of the Rayleigh-limit, the sagittal and tangential fields vary less than 0.2% of the focal length and distortion is less than 0.4%.

Although the invention has been described in considerable detail with reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be eifected without departing from the spirit and scope of the invention as described hereinabove.

I claim:

1. An objective lens having an equivalent focal length of f=100, and comprising four spaced optically aligned components, the front and rear components being simple negative meniscus elements concave toward the centrally located diaphragm, the two inner components being compound positive components encompassing the diaphragm space, the front compound positive component being a cemented doublet, the rear compound positive component I being a cemented triplet, the lens elements having substantially the following characteristics and spatial relations in which the lens elements are numbered from the front, N is the index of refraction for the D line, V is the index of dispersion and R, T and. S refer respectively to the radii of curvature of the lens surfaces, the axial thicknesses of 4 a the lens elements and the axial spacings between the lens elements, numbered by subscript from front to rear:-

Thleknesses Na V Radil and I spacings Lens.

R1=196.2 L1 1.62 60.3 Ti==4.0

S1=45.9 R =55.5 Lz' 1.73 51.0 Tz=27.2

R4=24.8 L|.. 1.62 53.9 T;=12.2

Rr=-Z85.2 Diaphragm Sr=5.4

Ra=-290.7 L4 1.57 57.4 T4=2.9 R7=3lt5 R =-26.1 Lu 1.72 29.3 Tu=16.8

S3=54.1 Rm=39.7 L1 1.66 40.4 T =l0.4 t. Rn=96.6

References Cited UNITED STATES PATENTS 2,781,695 2/1957 Klemt 350-220 FOREIGN PATENTS 7/1965 Germany.

DAVID SCHONBERG, Primary Examiner P. A. SACHER, Assistant Examiner 

